The present invention refers to an absorbent structure in an absorbent article such as a diaper, a pant diaper, an incontinence guard, a sanitary napkin etc. said absorbent structure comprises a compressed foam, which expands upon wetting. The invention further refers to a method of producing an absorbent article containing an absorbent structure according to the invention.
Absorbent articles of the above mentioned kind are intended to absorb body liquids such as urine and blood. Such absorbent articles usually have a liquid pervious topsheet, which during use is facing the wearer""s body. They further have a liquid impervious backsheet, e g a plastic film, a plastic coated nonwoven or a hydrophobic nonwoven, and an absorbent structure enclosed between the liquid pervious topsheet and the liquid impervious backsheet. The absorbent structure may comprise two or more layers such as liquid acquisition layer, storage layer and distribution layer.
It is desired that absorbent articles of the above mentioned kind are thin and discrete to use. It is further important that absorbent articles of the above mentioned kind have a high liquid acquisition capacity as well as liquid distributing and liquid storing capacity.
In order to obtain a good liquid acquisition capacity it is important that the liquid acquisition layer has a high momentaneous liquid acquisition capacity. Open, bulky structures with large capillaries have a high momentaneous liquid acquisition capacity and examples of such material are cellulosic fluff pulp of thermomechanic or chenithermomechanic (CTMP) type, chemically stiffened cellulosic fibers, synthetic fiber structures of different kind and porous foam materials.
It is previously known through U.S. Pat. No. 3,512,450, EP-A-0 293 208 and EP-A-0 804 913 to use a compressed foam material of regenerated cellulose, e g viscose, as an absorbent structure in an absorbent article of the above mentioned kind, e g a sanitary napkin. The article may then be made very thin and still have a high absorption capacity. The compressed viscose foam expands quickly i the z-direction when liquid is absorbed by the material when wetted. From EP-A-0 293 208 it is further known that such an absorbent structure can contain superabsorbent material.
As storage layer it is commonly used cellulosic fluff pulp with admixture of super-absorbents, i e crosslinked polymers with the ability to absorb liquid several times their own weight. In order to obtain a thin diaper with a maintained total absorption capacity, it is desired to increase the amount of superabsorbent material in the fluff pulp network. In order to make it possible to increase the amount of superabsorbent material it is for example through EP 0 532 002 in absorbent structures known to use superabsorbent material having a good liquid distributing capacity.
Through EP 0 212 618 and EP 0 478 011 it is known to use an absorbent structure that seen in its thickness direction has a gradually increasing concentration of super-absorbent particles, at which a higher concentration of superabsorbent material is localized to the portion of the absorbent structure that during use is placed closest to the liquid impervious backsheet. The use of such a structure attempts to reduce the risk for gelblocking and to improve liquid distribution. One problem with such a structure is that from a processability point of view it is difficult to apply the superabsorbent particles so that a gradually increasing particle concentration is achieved in the thickness direction.
The problem of providing an absorbent article which is comfortable and discrete to wear, at the same time as it has both a high liquid acquisition capacity and a high liquid distribution capacity, has been substantially eliminated by the present invention.
According to the invention there is provided an absorbent porous structure for use in a diaper, a pant diaper, an incontinence guard, a sanitary napkin etc. and which is provided with a liquid acquisition portion and a liquid storage portion, at which the liquid acquisition portion comprises a compressed polymeric open-cell foam which expands upon wetting, and which is characterized by the liquid acquisition portion and the liquid storage portion being an integrated unit, at which the liquid storage portion comprises a polymeric open-cell foam which may be the same or different from the foam in the liquid acquisition portion, and that the liquid storage portion also contains a superabsorbent material. In the portion of the liquid storage portion that is located closest to the liquid acquisition portion the amount of superabsorbent material is lower than in the portion of the liquid storage portion that is located furthest away from the liquid acquisition portion. One advantage of the invention is that the total absorption capacity of the absorbent structure is utilized to a higher degree than if the amount of superabsorbent material is the same in the entire liquid storage layer. In the upper part of the liquid storage layer it is important that the liquid has the ability to be distributed in the longitudinal direction of the structure from the longitudinal mid portion of the structure which coincides with the wetting area, out towards the longitudinal end portions of the absorbent structure. In the lower part of the liquid storage portion it is however mainly important that the absorption capacity is so high that the article has the ability to store so much liquid as possible without leaking.
Thus with the present invention there is obtained an integrated absorbent structure which has a high liquid acquisition capacity as well as a high liquid distribution and liquid storage capacity. An integrated absorbent structure is more advantageous than an absorbent structure comprising different layers since the joining step is eliminated, making the structure cheaper to manufacture. The problem of having a bad liquid transfer layer between different layers is further eliminated in an integrated structure. The reason for usually having a worse liquid transfer between different layers than in an integrated structure is that it is difficult to achieve a sufficiently good contact between different layers. Another advantage relating to a foam absorbent structure is that it is more flexible and pliable than a fibrous structure. Another advantage with a foam-formed structure is that it is easier to provide a uniform basis weight in the longitudinal and transverse direction of the structure. It has however proved to be difficult to provide a matformed fiber structure having a sufficiently uniform basis weight.
According to a preferred embodiment the amount of superabsorbent material increases gradually in the z-direction of the of the liquid storage portion from the part of the liquid storage portion that is located closest to the liquid acquisition portion to the part of the liquid storage portion that is located furthest away from the liquid acquisition portion. Such an embodiment is advantageous since it reduces the risk for gelblocking farther.
According to one embodiment the portion of the liquid storage portion that as seen in the z-direction is located remote from the liquid acquisition portion only comprises superabsorbent material.
According to an embodiment the superabsorbent material is a porous open-cell foam structure. The advantage of having the superabsorbent material in the form of a foam, is that it is possible to obtain liquid transport between the pores in the superabsorbent material. It is especially important that the superabsorbent material per se has the ability to transport liquid when the amount of superabsorbent is high, i e in the lower part of the liquid storage portion. When the superabsorbent material is in the form of an open-cell foam structure it is also possible that the absorbent material according to the invention only consists of the superabsorbent material. It is also possible that the superabsorbent material comprises a film-forming polymer, which forms a film coating on the pore walls of the foam. Another advantage of having the superabsorbent material in the form of a foam or a film-forming coating, is that such a Structure is easy to produce since the difficulties of applying superabsorbent particles in a thickness gradient are eliminated. In such a structure the problem of dusting caused by the smallest superabsorbent particles in the manufacture is eliminated.
The superabsorbent material can for example be based on polyacrylate. It is also possible that the superabsorbent material is based on cellulose or starch.
According to a preferred embodiment the compressed foam structure comprises a regenerated cellulose structure, so called viscose foam. An advantage with a foam of regenerated cellulose is that such a foam when wetted has a very high swelling ability in the z-direction of the structure. This involves that such an article can be very thin before wetting. It is also an advantageous material for articles that are to be shaped into a three-dimensional shape upon wetting, such as for example hump-shaped sanitary napkins. By the fact that the three-dimensional shape appears upon wetting it is possible to produce articles that still are thin and discrete before use.
According to an embodiment the regenerated cellulose foam structure also includes fibers. By incorporating fibrous elements in the regenerated foam structure an improved liquid distributing capacity is achieved.
According to one embodiment the foam structure in the liquid acquisition portion is in dry condition more compressed than the foam structure in the liquid storage portion.
The invention also refers to a method for producing an absorbent structure according to the invention. Such a structure is obtained by shaping a foam material, which is compressed and then dried. After drying the structure a monomer solution of superabsorbent material is added to one of the opposite sides of the foam material, as seen in the z-direction, at which the part of the compressed foam that is wetted by the monomer solution expands. The polymer solution is then polymerized and crosslinked. The structure may optionally be compressed further, after which it is finally dried.
The invention also refers to an absorbent article such as incontinence guard, diaper, pant diaper, sanitary napkin and the like and of the kind comprising a liquid pervious topsheet, a liquid Impervious backsheet and an absorbent structure applied there-between, said absorbent structure containing a structure as disclosed above.